From the state of the art, air pressure control systems are known for controlling the air pressure in tires of a motor vehicle. In these systems, an air pressure control device is included which is assigned to each wheel and these devices automatically measure the air pressure of the tires of the motor vehicle and announce at least a critical deviation from a desired air pressure to the driver of the motor vehicle. For this purpose, each air pressure control device transmits a measured pressure signal together with an individual identifier at regular intervals to a central unit of the motor vehicle. The transmission of an individual identifier together with the pressure signal is especially important because, in the air pressure control system, contactless data are transmitted from the wheel of the motor vehicle to the motor vehicle. Therefore, it must be precluded that air pressure data of a neighboring vehicle are received, for example, in heavy traffic and that erroneous announcements are made to the driver of the motor vehicle based on these data. This is made possible by the individual identifiers because the wheels of another motor vehicle would, of course, transmit different individual identifiers. In this central unit, value pairs of the form (identifier of the air pressure control device/wheel position) for each wheel of the motor vehicle are stored so that a conclusion can be drawn by a corresponding comparison in the central unit as to which identifier is transmitted with the corresponding pressure signal from which wheel position of the motor vehicle. A deviation of the transmitted pressure signal from a pregiven value at a wheel position is displayed to the driver of the motor vehicle by the central unit so that the driver can initiate suitable measures.
The embodiments show that an air pressure control system described above can only function without difficulty when the allocations (identifier of the air pressure control device/wheel position) are correctly stored in the central unit. Accordingly, it must, on the one hand, be ensured that this allocation does not change during the operation of the motor vehicle and, on the other hand, a new allocation must be provided after each change of tires on the motor vehicle. A method is known from U.S. Pat. No. 5,808,190 with which a new allocation can be undertaken after a change of tires on the motor vehicle. In order to carry out the method according to U.S. Pat. No. 5,808,190, it is necessary to determine the rotational speed of each wheel of the vehicle with the aid of a measurement value sensor which is disposed on the wheel of the vehicle and rotates therewith (for more information, see U.S. Pat. No. 5,808,190).